1. Field of the Invention
The present invention relates to a signal transmission circuit used for an information processing device or the like which transmits a serial signal at a high speed, and to an IC package and a mounting substrate.
2. Description of the Related Art
A conventional signal transmission circuit reduces jitter with the use of, for example, an equalizer (for example, refer to JP 08-297924 A).
A frequency dependency of the loss of a passive equalizer is a frequency dependency lost reverse to the loss of a transmission path, and the loss of the total pass characteristics is kept substantially constant regardless of the frequency. For that reason, the receive waveform of a receiver IC (integrated circuit) has substantially the same amplitude in any bits, and the jitter of its eye pattern is reduced. Because the total frequency components are uniformly attenuated, the eye opening amplitude becomes small. However, the conventional circuit that reduces jitter by using the passive equalizer is configured by a circuit that includes elements such as an inductance, a resistor, and a capacitor. Therefore, forming such a circuit within an IC leads to a problem in that an IC process is complicated, and forming the circuit on a substrate in the form of chip parts leads to a problem in that the number of parts and the mounted area are increased.
Also, since the gain of an active equalizer has the characteristic that compensates the loss of a transmission path, the total pass characteristics are small in the loss over the total frequencies. For that reason, the receive waveform of the receiver IC is substantially the same as the output waveform of a driver IC (integrated circuit), and its eye pattern is reduced in the jitter and large in the opening amplitude. However, the conventional circuit that reduces the jitter by using the active equalizer uses a dedicated IC, or its function is integrated in the receiver IC. The use of the dedicated IC adversely increases the number of parts and the costs. In the case where the function is integrated in the receiver IC, not only the complicated IC, the increased IC area, the microscopic IC manufacturing process, and the resultant increased IC costs are caused, but also the waveform that has passed through the active equalizer cannot be observed from the external. In addition, either case leads to a problem in that the power consumption is remarkably increased in order to obtain the gain.
In addition, the output waveform of the driver IC which has been subjected to pre-emphasis is larger in the amplitude than the normal output waveform in only the bits immediately after being inverted. For that reason, the eye pattern of the output waveform of the driver IC has two kinds of levels in both of high and low. When the output waveform is attenuated in the high frequency component due to the loss of the transmission path, the receive waveform of the receiver IC becomes original level in all of the bits, and its eye pattern is small in jitter, bringing the opening amplitudes to a small level. The output waveform of the drive IC which has been subjected to de-emphasis has a normal amplitude in only the bits immediately after being inverted, and in the case of the same data as previous data, the amplitude is made small. For that reason, the eye pattern of the output waveform of the driver IC has two kinds of levels in both of high and low. When the output waveform is attenuated in the high frequency component due to the loss of the transmission path, the receive waveform of the receiver IC becomes small amplitude level in all of the bits, and its eye pattern is small in jitter, bringing the opening amplitudes to a small level. However, the conventional circuit that reduces the jitter by using pre-emphasis or de-emphasis requires a comparator circuit for comparing data of two continuous bits, and in the case where data is continuous, a control circuit that changes the amplitude of a first bit or a second bit, as a driver IC output, and a power circuit that changes the voltage across an output transistor. This configuration leads to a problem in that the complicated IC, the increased IC area, the microscopic IC manufacturing process, and the resultant increased IC costs are caused.